Pyrrolmone purification



PYRRDLIDONE PURIFICATION Iemple Clayton, White Bear Lake, Minn, assignorto Minnesota Mining and Manufacturing Company, St. Paul, Minn., acorporation of Delaware N Drawing. Filed Mar. '3, 1958, Ser. No. 718,472

3 Claims. c1. 202-52) This invention relates to the purification ofpyrrolidone and particularly to a one-step process therefor.

It has heretofore been known that commercially avilable pyrrolidonecontains various impurities such, as water, ammonia, basic materials,butyrolactone andthe like contaminants. It'is known that the removal ofthese substances is desirable to produce'pyrrolidone polymer-- izable toa good grade of polypyrrolidone, and several methods have been devisedin an attempt to remove such impurities. For example, the removal ofwater by distillation of a forerun of pyrrolidone prior topolymerization is described in U.S. Patent 2,638,463; the formation of acrystalline hydrate'and subsequent drying is described in U.S. Patent2,802,777 and a combination of treatment with a carboxylic anhydridefollowed by distillation from base is described in US. Patent 2,806,856.

Each of these heretofore known procedures requires a multiplicity ofoperations involving considerable labor and sequential removal of basicimpurities and water or the incomplete removal of one of thesecontaminants. These processes further are not always directlyapplicableto commercial pyrrolidone, which may contain considerable discolorationand contain su bstantial amounts of impurities.

it is an object of this invention to provide a one-step process for thepurification of pyrrolidone. A further object is to provide pyrrolidonewhich is free from basic materials and water. Other objects will becomeapparent hereinafter.

It has been found that the above and other objects of this invention areaccomplished by distilling pyrroli done under reducedpressure fromphosphorus pentoxide.

' It is very surprising to find that such treatment does not result inextensive damage to the pyrrolidone as would have been predicted on thebasis of previous experience with phosphorus pentoxide. It is, forexample, well known that phosphorus pentoxide can only be used fordrying substances such as hydrocarbons and halogenated hydrocarbons andthat it will react with substances containing oxygen or nitrogen. It isalso known that, for example, acetamide is converted to acetonitrile bydistillation from phosphorus pentoxide. It is further known thatphosphoric acid forms complexes with many lower molecular weightcompounds. in view of these prior observations it is most remarkablethat a simple distillation under reduced pressure of pyrrolidone in thepresence of phosphorus pentoxide not only removes basic mate rials andwater but does so to produce pyrrolidone which is readily polymerizable.The product pyrrolidone is found to be somewhat less absorbent in theultra-violet than pyrrolidone distilled from potassium hydroxide,indicating that less unsaturation is present after treatment,

and that no substantial deleterious action leading to unsaturatedproducts has occurred.

There are further advantages to the process of this invention. It isknown that polymerization of pyrrolidone occurs in the presence of abase and that butylrollactone is an activator for the reaction. Hence itis 2,944,944 Patented July 12, 1960 processing to recover residualpyrrolidone if this is desirable, for example, by diluting with waterand isolating the pyrrolidone hydrate.

A still further advantage of the present invention is in the uniform,substantial neutrality of the product pyrrolidone. it is found that whendistilled from bases, pyrrolidone contains variable amounts of basicsubstances. Any such variations are detrimental to the subsequentpolymerization of the pyrrolidone since they introduce an uncontrolledvariable. It is found in the process of the presentinvention that asmall forerun is slightly acidic, perhaps due to concentration of carbondioxide, and the bulk of the distilled purified pyrrolidone issubstantially neutral. There is therefore no problem associated withpossible variability in results.

Broadly speaking, the process of the invention is carried out by addingto crude pyrrolidone an amount of phosphorus pentoxide in the range ofabout 0.2 to 20 parts per parts of pyrrolidone. The resulting mixture isthen distilled under reduced pressure. The pressure and correspondingtemperature used are not important, but it is preferred that thedistillation be conducted at pressures of the order of about 0.1 to 10mm. of mercury, and at temperature ranging from about 60 to about C.However, even at higher pressures and temperatures the pot residueremains unpolymerized and can be processed for recovery of pyrrolidoneas hereinabove described.

The invention having been thus described in general terms, it is nowmore specifically illustrated to show the best mode contemplated forcarrying out the invention without thereby being limited in scope.Herein, parts are by weight and inherent viscosities are determined bystandard methods at a concentration of about 0.2 g. in 100 ml. ofmetacresol.

Example 1 rolidone containing about 1 percent of water and having afaint amine-like mousy odor; The phosphorus pentoxide dissolves onagitation and the vessel is arranged for vacuum distillation through ashort Vigreux column. The pyrrolidone'is distilled collecting a smallforer un to 102 C. at about 1.4 mm. Hg (about 6%) and the main cut(about 86%) is collected at about 1.45 mm. Hg and 102 to 104 C. Theyellowish color of the original pyrrolidone is somewhat darkened in thepresence of the phosphorus pentoxide, but does not noticeably increasefurther other than that it is concentrated during the distillation. Theresidue remaining after the distillation is a brownish yellow oilymaterial which is miscible with water. When the aqueous solution of theresidue is made alkaline, the amine-like, mousy odor noticed in thecommercial pyrrolidone is quite strong clearly showing removal of thisimpurity.

The neutrality of pyrrolidone is conveniently determined by determiningthe pH of 1 percent solutions in distilled water. The following resultsare obtained on the above fractions and pyrrolidone purified by othermethods.

done. 7 It has a melting point of about 265 C. and

' pH of 1% inherent viscosity of2. 75 which is unaffected bytreataqueous ment at room temperature for 1 hour with either 1N solutionhydrochloric acid or 1N potassium hydroxide. When Forerun of process ofinvention 4-6 heated at 250 C. under high vacuum (about mm. Main cut ofprocess of invention 6.5-6.7 5 Hg) for 0.5 hour the loss in weight isabout 6 percent. Commercial pyrrolidone 8-11 When pressed between heatedplatens at about 250 C.

Purified by process of US. 2,802,777 9-11 it forms a clear, transparentflexible film. Purified by process of US. 2,806,856 It is evident thatthe amount of phosphorus pentoxide using propionic anhydride 7-9employed can vary over wide limits from an amount It is thus evidentthat the product pyrrolidone of this lolbarely suificieni react withimpurities large exinvention is substantially neutral and is superior inthat 6655 howevelj It IS comm9nly Ound conYemem f respect to products ofprevious processes obtained by a amount be flom about to about 9 timesP' multiplicity of operations. of Water present. A preferred range tsfrom aoout 3 to The product pyrrolidone is adequately pure for polyaboutlumps the Weight of Water. present Thus m merization by the proceduresdescribed in US. Patents .punficanon of a crude commerclal gyrrohdone2,739,959 and 2,809,958, for example, by dissolving 0.8 tammg about 1parcel)? of.water about 1 to 10.1) ercent percent of sodium therein andthen adding about 0.7 part of phosphorus pentoxlde 18 added Thlsmventlon conof an activator as acetyl pyrrolidone. Alternatively puretemplates that a lesser m for example percent sodium or potassiumpyrro-lidone may be prepared and may be employiid as m Examp 1e afurther reemployed as the alkaline polymerization catalyst together 20 iY of Water is to be effected. as a part of the polymer with anactivator. The following example shows the p procqdum In h a.case thephosphorus suitability of the purified pyrrolidone of this invention inP .1S.-part1cu1arly efiectlve. t removal of the basic a Processaccording to US] Patent 2,809,958 eniplo'yin lmpun-ues a P 1 of mPotassium hydroxide to generate the catalyst. i preFede the dlstlnatmnfrom phosphorus pentPXlde m I. e p 7 t 5 which case the amount ofphosphorus pentoxide used 1 Example 2 may be in excess of that necessaryto react'with the re- A vessel fitted for vacuum distillation, additionand l Water. having a thermometer to measure the temperature'of What 15clalme'd the contents is charged with 100 parts of the purified main Theprocess for the purification of pyrrohdone, cut pyrrolidone of Example 1and 215 parts of xylene Whlch compuses ed s Q pentoxfd? F (Merck Reagentdistilling to 1 0) Vacuum crude pyrrolidone, sub ectlng the mixture to dstillation and heat are applied and distillation of xylene comunderricduced pres sure"?nd P F Substannauy mences at about C. at about 18mm. Hg pressure. Punfied pyrmhdm m h dtsnnate' A solution of 2.2 partsof potassium hydroxide in 3.0 T procajssfor the Punficatmn of PYrmhd9neWh1Chparts of water is then added and the added water and 35 Compnsesadmlxmfg abqut to 20 Parts Welght of that formed by reaction to formpotassium pyrrolidone Phosphorus fm i Wlm 9 Parts by i s t of crude arecodistilled with the xylene. The temperature ofthe Pyrrohdone, Sublectmgthe f to 415911311011 under contents of the vessel rises gradually asthe xylene disprsssufaand colleFtmg Substantlauy neutral tils and whenit reaches 90 C. (at the same pressure) lfied Pyrrohdone the dlstlliategall the water and most of the Xylene are in the distillate. '40 jPunficatlon of Pyrrohdone Whlch The contents of the flask are cooled andtransferred to compnses admmmg f crude Pyn'ohdone an amount a closablecontainer (such as a bottle) and 0.73 part of of Phosphorus Pentoxldejin excess of that which would acetyl pyrrolidone is added and mixed in.Polymerizabe fi to reactpwlth the contamed in Said tion commencesimmediately with some evolution of heat Pyrrohdone, and sublecting themlxture to distillation and is permitted to proceed under ambientconditions 45 under reduced Pressurefor about 6 5 hours. The resultantblock of 01 mer is ';removed from the container (suitably by brgaki ngthe References Cased m the g of thls Patent 'bOttIe) andfaftercomminution is washed with 400 part UNITED STATES PATENTS portions ofWater, 0.5% aqueous acetic acid and with 2 745 34 Mertz May 5 1956 Wateruntil substantially neutral. The very nearly white 2,802,777 Lohr Aug 1319 57 p lym r h s all the desirable properties of polypyrroli- 2,806,856a Robinson Sept, 1957

1. THE PROCESS FOR THE PURIFICATION OF PYRROLIDONE, WHICH COMPRISESADMIXING PHOSPHOROUS PENTOXIDE WITH CRUDE PYRROLIDONE, SUBJECTING THEMIXTURE TO DISTILLATION UNDER REDUCED PRESSURE, AND COLLECTINGSUBSTANTIALLY NEUTRAL PURIFIED PYRROLIDONE IN THE DISTILLATE.